Microphone



Patented Aug. 18,

UNITED STATE s PATENT OFFICE "mcaornoNE y Barton A. Proaza, Lmhmoiit, N. Y., assigner tu B. A. Proctor Company, Inc.,-New

' a corporationof New York I York, N. Y1;

Applieation December 5, 1939, serial No. 307,560

n claims.` (ci. 17e-4415.5)

,n This invention relatesyto microphones for con` verting `sound energy into electrical energy f The invention hasutility in connection with fpublic address systems, radio, telephony, sound recording, and,lin,fact, any purpose for which a "microphone can beused. I c

, It isan object ofthe invenuuto provide a microphone which is highly sensitive and which I responds with a high degreeof Ifidelity to variations of sound frequency and intensity.

It is a further object ofthe invention to pro- ",vide a microphoneemployinga `vibratory diaphragmlhaving electrical and `magnetic", parts associated with it,` and tojIenclose and sealA the electrical and magnetic parts against ingress of dirt and" moisturein such manner thatno substantial back pressure will be developed against `the diaphragm at any time.I I

`A further object fof the inventionis to provide I a" microphone structure which is I simple andI `perforated s material is formed with `a flange I4 which `bears against the ring II for clamping thediaphragm I inplace. A retaining ring I5 is threaded onto the shell I andis formed to` overlie the shield I plate I3, being effective to hold the shell, the

, diaphragm I0, and the shield plate I3 inassembled relation and clamped firmly to one an-` other., The retaining ring I'5 `extends only a short distance .inwardjover the shield plate I3,

economical tomanufacture and `which sturdy" and dependable in use.

. `Other objects `and advantages will hereinafter appear. l I" The single figure ofthe drawing discloses in I section a microphone embodying the invention.

The illustratedfmicrophone comprises a cupbeing formedwith a large central opening I6 which leaves the shield plate I3` almost fully exposed to the speaker. I

The diaphragm` IIJ ,has cemented to it a small coil II'I composed ofI a `multiplicity of turnsof fine wire. The coil I1 isoscillated longitudinally in the space beteween the boss 5 and the plate 1.

The plate 1 forms one pole piece of the composite magnet made up of theplate 1, the shell I, and the blocks 3 `and `Land the boss 5 forms the other pole piece' of the magnet.y The coil, therefore, is arranged to move in the region of maximum flux intensity. f Y n l Movementof the coil toward the rightv will induce current uto ow in one `direction through Ithe coil, and movement of the coil toward the left wiu `induce `current to new in the other dilike shell member` I Aof magnetic material` such as `hard steel;` A bolt! is passed throughthe back I of the member I` and through a1blockl3 of magnetic material, and is threaded into a block 4 of magnetic material for clamping the shell and the blocks firmly to one another. The` block 4 terminates in a round boss 5 which has a circular bore 6" formed centrally thereof. This hub`5 constitutes one pole piece ofv a composite structure of which the block 3 and the shell I also form ele-- ments. A plate `or disc I of magnetic material is fixed in the mouth ofthe shell I, being fitted into an internal rabbet` 8` formed in the shell. The

plate 'I is formed with a central `opening 9 which is concentric with theboss` 5 and which extends around the boss 5 ata short distance from it.

A flexible diaphragm magnetic material is disposed across the mouth I; of the shell I and secured against the forward face of the shell. The diaphragm is maderigid at .its outermargin by the spinning around such margin of a ring II of non-magnetic metal. The

diaphragm includes an annular area which is corrugated, the alternate ridges and valleys extending circularly `and concentrically around the center ofthe diaphragm. The central portion of the diaphragm is pressed outward or forward to form a substantially rigid Iboss I 2. I

` "respond in intensity to the intensity Lof the diarection through the coil. The current impulses.

thus` generatedwill respond in frequency to the Ifrequency of the diaphragm vibrations, and will phragm vibrations. Lead wires I8 and I9 areconnected toIopposite endsIof the` coil` wire. Theselead wires are cemented to the rear facev of the diaphragm III and extend through a passage 2|) formed in the shell I. The wires I8 and AI9 maybe connected in the conventional manner for utilization of the III of resilient, nonvoice current which has -coil I1. I

It is not desirable that air shall be trapped behind the diaphragm` III in` such a way as to create back pressure against the diaphragm. For this reason the plate 'I isformed with a number of holes 2| and the shell I is formed with `been induced in the `a number of holes 22.

In order, howeventhat the current inducing `parts may be protected from dirt, moisture and other deteriorating atmospheric constituents,

means are provided` for sealing such parts. A`

plate 23, which maybe of any suitable material,

is aixed within the shell I against an internal shoulder llto form a sealed joint with the shell. The plate 23 is formed with a central opening 25 which fits the block` 3I and forms Ia sealed jointI eid 'plate `Is `of non-magnetic I therewith, and with a series of openings 2l. A /diaphragm 21 which is impervious to dirt and atmospheric moisture and is formed of highly flexible material, such as sheet rubber, is cemented to the solid margins of the plate 23 adjacent the shell I and the block 3 and has its slack intermediate portion bowed or bellied to the rear as illustrated. The diaphragm 21 forms an absolute seal against ingress of atmospheric moisture and dirt, but'is freely capable of distortion so that no substantial back pressure of air against the diaphragm l can develop at any time.

I have described what I believe to be the best I embodiments of my invention. I do not wish, however, to be confined to f,the embodiments shown, but what I desire to cover by Letters Patent is set forth in the appended claims.

I claim:

1. A microphone comprising, in combination, a flexible vibratory diaphragm, means secured t0 the central portion of the diaphragm and responsive thereto for inducing electrical currents, and means including the diaphragm for housing the current-inducing means and for protecting `the current-inducing means against exposure to constituents of the atmosphere, said housing and protective means including a slack, sealing member of freely, flexible sheet material which is impervious to dirt and moisture and a supporting means arranged to support the sealing member at the rear of the diaphragm and in alignment therewith and spaced therefrom by a substantial distance.

2. In an acoustic device, in combination, a cup-like shell, a center post extending axially vwithin the shell from the base of the shell, a plate aillxed in the mouth of the shell, said plate having a central opening through which the center post extends concentrically to define a thin,

v annular space of uniform thickness, all of said shell, said partition plate lying wholly within the shell-and formed with a series of holes in an annular portion thereof, and a freely flexible, diaphragm impervious to dirt and moisture and composed of non-metallic material secured to the inner and outer margins 0f the partition plate in position to completely cover the holes therein.

3. A microphone comprising, in combination, a cup-like shell, and a flexible, Vibratory diaphragm secured across the front of the shell and forming therewith a chamber which is completely closed save that the shell is open to the atmosphere at the rear end thereof, means in the chamber associated with the diaphragm and cooperative therewith for inducing electrical currents, and sealing means disposed wholly within said shell for completely preventing access Of atmospheric constituents to the forward portion of the chamber, said sealing means including a slack sealing member of freely flexible material impervious to dirt and moisture.

4. An acoustic device, comprising, in combination, a cup-like shell, a center post extending axially within the shell from the base of the shell toward the front thereof, a plate aflixed in the front end of the shell, said plate having a central opening through which the center post extends concentrically to define a thin, annular space of uniform thickness, all of said parts being composed of magnetic material for forming a composite magnetic structure, the plate having holes formed in it between the central opening and the outer boundary, and said shell being opened to the atmosphere at the rear end thereof, a flexible vibratory diaphragm covering the mouth of the shell and cooperating with the shell to form a chamber, and a freely flexible diaphragm formed of non-metallic material impervious to dirt and moisture disposed within and transversely of the shell far behind said plate and sealing the forward portion of said chamber against communication with the atmosphere.

5. An acoustic device comprising, in combination, a cup-like shell formed of magnetic material and provided with an inwardly extending annular pole piece and a second pole piece having an end disposed concentrically within said annular poleA piece, a vibratory diaphragm mounted on and extending across the front portion of the shell and having a voice coil disposed between 'said pole pieces, and means comprising a freely flexible rubber diaphragm disposed transversely between the second pole piece and the shell and arranged to prevent air in the rear portion of the shell from passing forwardly and coming in contact with the voice coil.

BARTON A. PROCTOR. 

